This invention relates to a clutch for use with a rotary cutting tool. More particularly, this invention relates to a single clutch which achieves two functions performed by separate clutches in the prior art.
Rotary cutting tools are known which include a rotary motor driving a tool, where the tool is brought vertically into a surface to be cut. A manual drive was often utilized to bring the rotary tool vertically downwardly into the surface to be cut.
Recently, drive motors have been utilized to move the tools vertically. These prior art tools have typically utilized a first selectively actuatable clutch which may be engaged to transmit drive from a motor to move the tool vertically. When in an unactuated position the clutch does not transmit drive from the motor to the tool.
In some cases these prior art tools may have included a second clutch to provide a slip force that sets a predetermined maximum drive force or torque between the drive motor and the rotary tool. Should this predetermined force be exceeded, the second clutch typically has two members which move relative to each other such that drive is not transmitted from the motor to the tool. The use of these two separate clutches does achieve two important functions, but complicates the assembly.
In some prior art arrangements, ball clutches have been utilized as the second clutch. In a ball clutch, movement is transmitted between two clutch members by the engagement of balls associated with one clutch member which are received in notches in the other clutch member. The balls are biased into the notches to provide a contact surface which transmits drive. Should a drive force between the balls and notches exceed a predetermined slip force the balls move against the bias force out of the notches. Increasing the bias force increases the slip force. With wear, the size of the notches increases, and it becomes necessary to increase the biasing force to achieve a predetermined slip force. In particular, notches which are conical and shaped by a drill bit are utilized, and the edges of these notches wear and become rounded such they do not grip the balls as adequately as they do when new.
Ball clutch assemblies have been developed in which this biasing force is adjustable. Examples of adjustable force ball clutch assemblies are disclosed in U.S. Pat. Nos. 4,812,089 and 4,898,265. In these devices members move against a spring to compress or expand the spring and change the force biasing the balls into the notches. Neither of these patents are disclosed with a rotary cutting tool. Further, neither of these patents disclose selectively engageable clutches.
A rotary cutting tool may encounter an obstruction or may bind should the tool encounter a surface which is difficult to cut, and it is important that a maximum slip force be maintained on the ball clutch. In several prior art rotary tools the use of an adjustable force ball clutch may not be advisable since if the bias force was inadvertently set too high, drive forces between the clutch members above a desired maximum slip force could occur.
It is an object of the present invention to disclose a rotary cutting tool having a clutch assembly in which a single clutch element provides both a selectively actuatable clutch and a slip force. It is further an object of the present invention to disclose an adjustable force clutch which is utilized in a rotary cutting tool.